Re: [PATCH v3 4/4] objtool: orc_gen: Move orc_entry out of instruction structure

[Julien Thierry]

On 7/30/20 11:03 AM, peterz@xxxxxxxxxxxxx wrote:
> On Thu, Jul 30, 2020 at 10:41:43AM +0100, Julien Thierry wrote:
> > One orc_entry is associated with each instruction in the object file,
> > but having the orc_entry contained by the instruction structure forces
> > architectures not implementing the orc subcommands to provide a dummy
> > definition of the orc_entry.
> >
> > Avoid that by having orc_entries in a separate list, part of the
> > objtool_file.
>
> > diff --git a/tools/objtool/orc_gen.c b/tools/objtool/orc_gen.c
> > index 66fd56c33303..00f1efd05653 100644
> > --- a/tools/objtool/orc_gen.c
> > +++ b/tools/objtool/orc_gen.c
> > @@ -9,18 +9,33 @@
> >   #include "check.h"
> >   #include "warn.h"
> >   
> > +struct orc_data {
> > +	struct list_head list;
> > +	struct instruction *insn;
> > +	struct orc_entry orc;
> > +};
> > +
> >   int create_orc(struct objtool_file *file)
> >   {
> >   	struct instruction *insn;
> >   
> >   	for_each_insn(file, insn) {
> > -		struct orc_entry *orc = &insn->orc;
> >   		struct cfi_reg *cfa = &insn->cfi.cfa;
> >   		struct cfi_reg *bp = &insn->cfi.regs[CFI_BP];
> > +		struct orc_entry *orc;
> > +		struct orc_data *od;
> >   
> >   		if (!insn->sec->text)
> >   			continue;
> >   
> > +		od = calloc(1, sizeof(*od));
> > +		if (!od)
> > +			return -1;
> > +		od->insn = insn;
> > +		list_add_tail(&od->list, &file->orc_data_list);
> > +
> > +		orc = &od->orc;
> > +
> >   		orc->end = insn->cfi.end;
> >   
> >   		if (cfa->base == CFI_UNDEFINED) {
>
> This will dramatically increase the amount of allocation calls, what, if
> anything, does this do for the performance of objtool?

I guess I forgot about the usecase of running objtool on vmlinux...

On a kernel build for x86_64 defconfig, the difference in time seems to 
be withing the noise.

But I agree the proposed code is not ideal and on the other we've tried 
avoiding #ifdef in the code. Ideally I'd have an empty orc_entry 
definition when SUBCMD_ORC is not implemented.

Would you have a suggested approach to do that?

Thanks,

--
Julien Thierry